1. Field of the Invention
This invention relates to blood extracting devices.
2. Description of the Prior Art
Various methods and devices are known to those of ordinary skill in the art for extracting blood from the vein of a patient. The simplest prior art method requires a cannula which pierces into the vein. The blood flows out of the other end of the cannula and is collected in a vessel. This method does have the advantage that the blood flows freely and without a loading by a subatmospheric pressure with a relatively low flow velocity. On the other hand this method does have the disadvantage that the vein must be dammed excessively by strangulating, and this actually is not desired. A further disadvantage of this method is that the operation is quite unclean, since it generally is not possible to completely connect the blood flowing from the other end of the cannula, so that the patient's dress or the bed-clothes is contaminated with blood.
According to another prior art method, blood is extracted by means of a conventional injection syringe, and this is done by introducing the cannula applied thereto into the vein and by retracting the piston in the cylinder of the syringe. In this method or use of this device an extensive damming is not necessary and a damming of the blood even is superfluous. On the other hand the high vacuum in the syringe cylinder resulting by a quick retraction is detrimental, since the blood may form and is damaged in its colloidal structure. Also a high flow velocity of the blood in the cannula results, when the retraction is carried out too quickly, and this may result in a hemolysis by the turbulence caused thereby.
A further disadvantage is that after piercing the cannula point into the vein both hands are required for loading the syringe. When doing so a damaging of the opposite vein wall may result by the cannula point when the operation is carried out impatiently or when the patient is impatient.
Finally, the loading of a syringe, in particular with narrow cannulas, requires a certain effort which is tiring for weaker persons and again may result in impatience and thus an injury of the vein wall.
Since sometimes devices have also been used for extracting blood in which the attachment socket for applying the cannula is not secured to one end of the cylinder like in the foregoing mentioned injection syringes, but to the piston rod provided with a continuous longitudinal bore, that piston rod being connected to the piston likewise containing a through-bore, while the cylinder is defined as a tubule closed at one side which may subsequently be used for centrifuging the extracted blood. Although with such a device when extracting blood an excessively high vacuum does not result readily in the receiving cylinder, because this device is easier to manipulate and permits a more sensitive operation, depending on circumstances a high vacuum and a high flow velocity may result by a quick manipulation. With this device both hands are also needed for extracting the blood.
The foregoing mentioned two blood extraction devices would be at an optimum if it would be successful to eliminate the disadvantages of the manipulation with both hands and the disadvantages resulting by a hurried handling.
Now apparatus has become known for loading the foregoing mentioned blood extracting devices, wherein spring means withdraw the piston of the blood extracting device partially from the cylinder thereof upon being relieved. A helical compression spring is used as spring mean's. This spring is initially biased and is released after the cannula of the blood extracting device has been introduced in the vein, so that the spring relieves and loads the blood extracting device. This conventional apparatus has the major disadvantage that the force of the biased spring is very high and accordingly moves the piston of the blood extracting device joltingly in the moment of releasing and in doing so causes an undesired subatmospheric pressure pulse which damages the blood extracted and might even result in a foaming thereof.
In another conventional apparatus for loading blood extracting devices a small electric motor is used which is driven by a battery disposed in the apparatus. This apparatus is extremely complicated and thus on the one hand costly, on the other hand prone to defects and has a weight which renders difficult its operation.